1. Field of the Invention
The present invention relates to a copolymer, a polymer composition and a polymer light-emitting device (hereafter, referred to as “polymer LED”).
2. Description of the Related Art
Electronic materials using polymer compounds are variously investigated for electronic devices. Among them, copolymers having a substituted or non-substituted repeating unit consisting of fluorene-2,7-diyl group (fluorene repeating unit) are studied since a light emitting layer etc. in a light-emitting device can be formed by a coating method, for example, as a polymer light-emitting material (polymeric fluorescent substance).
As a copolymer having a fluorene repeating unit, for example, J. Mater. Sci. Mater. Ele., volume 11, page 111 (2000) discloses a copolymer consisting of one kind of fluorene repeating unit, and a repeating unit, such as phenylene or naphthalene-diyl. Moreover, as a copolymer consisting of two kinds of fluorene repeating units, for example, Adv. Mater. volume 12, page 362 (2000) discloses a 1:1 copolymer of 2,7-[9,9-bis(2S-2-methylbutyl)]fluorene and 2,7-(9,9-bisdioctyl)fluorene.
In order to produce a light emitting layer of a light-emitting device uniformly by a coating method using a fluorene copolymer as a polymeric fluorescent substance, excellent solubility of the copolymer in an organic solvent is required. Moreover, in order to improve the stability of the light-emitting device, high glass transition temperature of the copolymer is required.
However, the above known fluorene copolymers still have insufficient solubility in an organic solvent or insufficient glass transition temperature.
The object of the present invention is to provide a copolymer comprising a fluorene repeating unit, having an excellent solubility in an organic solvent, and a high glass transition temperature in good balance, and to provide a polymer LED of high performance, such as low-voltage driving and high luminance, with using the copolymer.
As a result of intensive studies to solve the above-mentioned problems, the present inventors found that a copolymer having two kinds of fluorene repeating units, and a repeating unit, such as phenylene, or a copolymer having two kinds of fluorene repeating units in a specific ratio, has an excellent solubility in an organic solvent and a high glass transition temperature in sufficiently good balance, and completed the present invention.
Moreover, as a result of further study, the present inventors found that a copolymer having a polystyrene reduced number average molecular weight of 103-108, and exhibiting fluorescence in the solid state, wherein the below defined value T1ρH/<T1ρH> is 0.35 or less, has an excellent solubility in an organic solvent, and that a polymer composition comprising two kinds or more of copolymers having a polystyrene reduced number average molecular weight of 103-108, and exhibiting fluorescence in the solid state, wherein the below defined value T1ρH/<T1ρH> is 0.35 or less, can give a uniform film.